Giant tiger prawn invades Gulf of Mexico

Huge, hungry prawns from Asia have exploded across the U.S. Gulf Coast this year, potentially posing a serious threat to smaller native species.

PRAWN STARS: Asian tiger prawns like this one can grow up to a foot long, have voracious appetites and frequently carry disease. (Photo: Louisiana Dept. of Wildlife and Fisheries)

The giant tiger prawn is more than just a jumbo shrimp. It's a huge, hungry and highly invasive species that could pose a jumbo problem for the already embattled Gulf of Mexico ecosystem. And according to wildlife officials along the U.S. Gulf Coast, it had a very big year in 2011.

Formally named Penaeus monodon, the tiger prawn inhabits the Indian and Pacific oceans from Africa to Australia. It's more predatory than many similar species, hiding during the day and hunting at night. It also has a ravenous appetite, helping some adults grow up to 14 inches and 23 ounces. Small groups have haunted the U.S. Gulf and Atlantic coasts since 2006, turning up in the Carolinas, Georgia, Florida and Alabama. Louisiana reports about 25 to 30 per year.

But according to Houma Today of Terrebonne Parish, La., there were nearly 100 reports of tiger prawns this fall in Louisiana alone, with one dock counting 100 individuals. Texas' first-ever specimen was caught in June, the Houston Chronicle reports, followed soon after by four more. And the U.S. Geological Survey lists eight tiger prawns this year in Mississippi, 11 in Florida and 18 in Alabama — compared with zero, two and zero respectively in 2010. The USGS listed 42 such reports nationwide in 2009, and just 18 in '08.

While no one is sure what kind of ecological impact tiger prawns could have in the Gulf, their appetite isn't the only concern. The species is also a known carrier of at least 16 different viruses, including white spot, yellowhead and others that can kill shrimp. Experts say this array of dangers may threaten not only the Gulf's native brown and white shrimp populations, but also some crabs and oysters.

"It has the potential to be real ugly," Leslie Hartman, a biologist with the Texas Parks and Wildlife Department, tells the Houston Chronicle. "But we just do not know." Fellow biologist Marty Bourgeois of Louisiana's Department of Wildlife and Fisheries echoes that sentiment. "There's a certain unknown about what ecological impacts that something non-indigenous like this can have on the local environment," he tells Houma Today. "But it is somewhat alarming that these reports have suddenly ramped up."

In addition to its vast native habitat, the tiger prawn is also one of the most widely cultivated species of shrimp or prawn on Earth, according to the U.N. Food and Agriculture Organization (see chart below). The top producers are mainly in Asia, but it's farmed around the world. Scientists aren't sure where the Gulf invaders came from, although a leading theory suggests they escaped from aquaculture facilities.

A South Carolina farm accidentally released a cluster of tiger prawns in 1988, the Associated Press notes, and they may have found a way to spread without detection until now. That's not uncommon with invasive species, which often lie low for generations before exploding across their new habitat. Asian carp likely escaped from Arkansas fish farms in the 1970s, for example, but didn't become a regional menace until years afterward (and scientists now fear a similar pattern in the Great Lakes).

A migration from South Carolina would still be challenging, though, and there are other possibilities. Tiger prawns could have fled U.S. aquaculture farms during hurricanes Katrina and Rita in 2005, for instance, or from operations in the Caribbean Sea and Central America during more recent storms. Scientists plan to conduct genetic tests on the newly caught prawns to determine their origin, the Chronicle reports, but at least 60 specimens will be needed to ensure accuracy.

The case of loose tiger prawns also casts a broader spotlight on Gulf Coast aquaculture, which the Obama administration authorized in 2009 despite criticism from environmental and fishing groups. Diseases like white spot naturally exist at low levels in the wild, but — much like diseases at industrial cattle, poultry or hog farms — they can grow more virulent when their hosts are densely packed together.

While regulations are generally stricter for farming non-native species in the U.S., it's hard to completely prevent escapes from happening — especially amid a hurricane or flood. And even if the escaped prawns don't devastate native shrimp with viruses, they still eat many of the same food sources, potentially putting them in direct competition. They're also known to eat some smaller crustaceans.

It's too soon to know the scope of the problem, but a reproducing population of tiger prawn in the Gulf could easily be disastrous. The region is already home to a menagerie of invasive species — from tilapia and lionfish to zebra mussels and nutria — and parts of it remain wrecked by the 2010 BP oil spill. An alien predator as big and prolific as the tiger prawn is the last thing such a fragile ecosystem needs.

Still, there may be a silver lining — for humans, at least. Campaigns promoting invasive species as cuisine have gained steam in recent years, whether it's lionfish in Miami or Asian carp in Memphis, and there's a reason tiger prawn are so widely cultivated. The big, meaty crustaceans command an even higher market price than native brown shrimp, the Chronicle points out, raising the possibility that they too could become a profitable Gulf Coast commodity.

"It could be another crop," Hartman explains, "but at the expense of our native crop."